[phenixbb] baton build in coot

Dear Friends, How does CA ZONE > MAIN CHAIN under 'other modeling tools' in coot work? I was trying to rebuild main chain atoms for 3 residues(8,9,10) using CA ZONE > MAIN CHAIN. when I click on one atom in residue 8 and then one atom in residue 10, it failed with a message that says the zone is too short. I increased the zone to 5 residues, still same failed message. Also, is it possible to move an atom in coot? Thanking you in advance for your reply. Raja